A low cost Arduino shield with this display, controller and backlight http://www.sparkfun.com/products/10168 and some buttons would be awesome! I have been using the display for a while now and it is relatively easy to use (even without using the library) and very cheap.
it would serve as a low cost low power easy to use alternative to the color lcd shield: http://www.sparkfun.com/products/9363
it could be used for endless things, a uno and this (still non existant) shield would be all you need for a nice little clock, usb enabled display to show stats about your computer/server, quickly and easily displaying lots of sensor data in a breadboard setup…
i imagine this can be sold for way less than 30 dollars and become very popular with all kinds of people. if it ever becomes a reality i’m willing to write a library for it in my spare time.
Building a product on the Nokia 5110 that Sparkfun has might not be a great idea. I have purchased two and neither have worked. The connection from the LCD to the breakout board is via those rubbery connectors that have fine wires embedded in them. They rely on being compressed to make contact along the raw edges. The issue is the the Sparkfun boards are warped and the distribution of force is not equal and hence the connections are not good. You can read more issues from others as well in the comments on the product page you liked to as well as in the Forum.
I am not disputing your desire for a cheap LCD display with a few buttons. I had the same need and purchased these cheap LCDs at first. Eventually moving to the Color LCD (http://www.sparkfun.com/products/8600). Only to find that this product has a defect in the power boost converter for the backlight. Luckily a simple one resistor fix was enough to solve that issue.
the shield would be a great chance for sparkfun to fix the problems with the lcd breakout design and as there would be more space on a shield compared to the breakout they wouldn’t have to cram the electronics underneath the display thus putting less strain on it (if that is the reason for the breakout being warped a bit).